Maximum ratio combining in broadcast OFDM systems based on multiple receive antennas

ABSTRACT

Systems and methods are provided for enhancing signal quality at receivers in a wireless network. In one embodiment, an antenna is selected from a subset of antennas based on a signal quality parameter such as received signal power or signal-to-noise ratio (SNR). In another embodiment, multiple antennas are applied to independent signal processing paths for the respective antennas where output from the paths is then combined to enhance overall signal quality at the receiver.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/721,373 filed on Sep. 27, 2005, entitled“SWITCHING DIVERSITY IN BROADCAST OFDM SYSTEMS BASED ON MULTIPLE RECEIVEANTENNAS” the entirety of which is incorporated herein by reference.

BACKGROUND

I. Field

The subject technology relates generally to communications systems andmethods, and more particularly to systems and methods that enhancereceiver performance in a wireless system by exploiting multipleantennas at the receiver.

II. Background

One technology that has dominated wireless systems is Code DivisionMultiple Access (CDMA) digital wireless technology. In addition to CDMA,an air interface specification defines FLO (Forward Link Only)technology that has been developed by an industry-led group of wirelessproviders. In general, FLO has leveraged the most advantageous featuresof wireless technologies available and used the latest advances incoding and system design to consistently achieve the highest-qualityperformance. One goal is for FLO to be a globally adopted standard.

The FLO technology was designed in one case for a mobile multimediaenvironment and exhibits performance characteristics suited ideally foruse on cellular handsets. It uses the latest advances in coding andinterleaving to achieve the highest-quality reception at all times, bothfor real-time content streaming and other data services. FLO technologycan provide robust mobile performance and high capacity withoutcompromising power consumption. The technology also reduces the networkcost of delivering multimedia content by dramatically decreasing thenumber of transmitters needed to be deployed. In addition, FLOtechnology-based multimedia multicasting complements wireless operators'cellular network data and voice services, delivering content to the samecellular handsets used on 3G networks.

The FLO wireless system has been designed to broadcast real time audioand video signals, apart from non-real time services to mobile users.The respective FLO transmission is carried out using tall and high powertransmitters to ensure wide coverage in a given geographical area. In abroadcast Orthogonal Frequency Division Multiplexing (OFDM) system suchas FLO, respective OFDM symbols are organized into frames havingphysical layer packets that are encoded with a Reed-Solomon (R-S) codeand distributed across the frames to exploit time-diversity of a fadingchannel. Time diversity implies that several channel realizations areobserved over the duration of each code block and hence, the packets canbe recovered even if there was a deep fade during some of the packets.However, for very low speeds of a mobile handset or receiver (smallDoppler spread), the channel coherence time is long compared to thetime-span of a Reed-Solomon code block and thus, the channel evolvesslowly. As a result, little time-diversity can be gained within aReed-Solomon code block (for FLO, a Reed-Solomon code block spans acrossfour frames. As a result, the duration of a Reed-Solomon code block isapproximately 0.75 second). The prior approach was to use a singlereceive antenna on the handset. However, as the speed of the mobilehandset (or Doppler spread) changes, especially for low Doppler spreadscenarios, the performance of single receive antenna FLO receiverarchitectures can degrade.

SUMMARY

The following presents a simplified summary of various embodiments inorder to provide a basic understanding of some aspects of theembodiments. This summary is not an extensive overview. It is notintended to identify key/critical elements or to delineate the scope ofthe embodiments disclosed herein. Its sole purpose is to present someconcepts in a simplified form as a prelude to the more detaileddescription that is presented later.

Systems and methods are provided to facilitate receiver performance in abroadcast wireless network by employing multiple antennas at thereceiver that cooperate to enhance signal quality in the receiver. Inone embodiment, at least two antennas are employed at the receiver,where the antennas are monitored and switching components are utilizedto select an antenna from a subset of antennas. The selected antennafrom the subset generally provides the strongest signal power, highestsignal-to-noise ratio (SNR), or other signal quality parameter at thereceiver thus enhancing the quality of signal to be processed at thereceiver. In another embodiment, a dual-track (or multi-track) approachis applied where multiple antennas are adapted to separate receiverprocessing paths. Respective output from the paths is then combined inwhat is referred to as a maximum ratio combining technique to enhanceoverall signal quality at the receiver.

To the accomplishment of the foregoing and related ends, certainillustrative embodiments are described herein in connection with thefollowing description and the annexed drawings. These aspects areindicative of various ways in which the embodiments may be practiced,all of which are intended to be covered.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram illustrating a wireless networkreceiver system.

FIG. 2 is an example receiver switching component that employs multipleantennas to enhance signal quality.

FIG. 3 is illustrates example switching component processing options fora wireless receiver.

FIG. 4 illustrates an example multi-path processing component for awireless receiver system.

FIG. 5 is a diagram illustrating example network layers for a wirelessreceiver system.

FIG. 6 is a diagram illustrating an example data structure and signalfor a wireless receiver system.

FIG. 7 illustrates an example process for a wireless receiver system.

FIG. 8 is a diagram illustrating an example user device for a wirelesssystem.

FIG. 9 is a diagram illustrating an example base station for a wirelesssystem.

FIG. 10 is a diagram illustrating an example transceiver for a wirelesssystem.

DETAILED DESCRIPTION

Systems and methods are provided for enhancing signal quality atreceivers in a wireless network. In one embodiment, an antenna isselected from a subset of antennas based on a signal quality parametersuch as received signal power or signal-to-noise ratio (SNR). In anotherembodiment, multiple antennas are applied to independent signalprocessing paths for the respective antennas where output from the pathsis then combined to enhance overall signal quality at the receiver. Byemploying multiple receive antennas, and selecting from a subset ofantennas or providing independent processing paths for the antennas,signal quality and hence performance of the receiver can be improved inthe wireless network.

As used in this application, the terms “component,” “network,” “system,”and the like are intended to refer to a computer-related entity, eitherhardware, a combination of hardware and software, software, or softwarein execution. For example, a component may be, but is not limited tobeing, a process running on a processor, a processor, an object, anexecutable, a thread of execution, a program, and/or a computer. By wayof illustration, both an application running on a communications deviceand the device can be a component. One or more components may residewithin a process and/or thread of execution and a component may belocalized on one computer and/or distributed between two or morecomputers. Also, these components can execute from various computerreadable media having various data structures stored thereon. Thecomponents may communicate over local and/or remote processes such as inaccordance with a signal having one or more data packets (e.g., datafrom one component interacting with another component in a local system,distributed system, and/or across a wired or wireless network such asthe Internet).

FIG. 1 illustrates a wireless network receiver system 100 that employsan antenna subset 110 at the receiver, where the antenna subset 110includes two or more antennas. As illustrated, a first receiverconfiguration is illustrated at 120 where a monitor component 130measures signals from the antenna subset 110 and a switch component 140selects an antenna to receive and further process a wireless signalbased on the measurement from the monitor component. In another receiverconfiguration at 150, a separate signal path 160 can be adapted to eachantenna in the subset 110, where a combiner 170 produces an optimizedsignal from the combination of signals provided by the subset.

With respect to the first receiver configuration 120, by employing twoor more diversity antennas and switching to the antenna with strongerReceived Signal Strength Indication (RSSI) or higher Signal-to-NoiseRatio (SNR), the configuration 120 exploits antenna diversity andimproves receiver performance. In one example, this is beneficial forslow fading channels to compensate for the lack of time-diversity. Dueto the bursting nature of Forward Link Only (FLO) transmissions, theRSSI measurement, SNR calculation (or other parameter measurement) andantenna selection is performed before the start of Multicast LogicalChannel (MLC) processing. Thus, decoding of respective OFDM symbols ofinterest are generally not affected. The added power consumption forRSSI measurement or SNR calculation and antenna selection is also fairlyinsignificant. In the presence of antenna differential, switchingdiversity can be turned off at high Doppler spread so that performancein this scenario should not be impacted. The RSSI can be calculatedbased on Low Noise Amplifier (LNA) state information and the AutomaticGain control (AGC) loop accumulator values in a straightforward manner.

It is noted that in one approach, an algorithm can be employed toestimate noise variance at the receiver. The base-band compositereceived power which includes power from both signal and noise is alsocomputed. The ratio of the composite received power to the estimatednoise variance is taken and serves as an indication of the received SNR.The antenna with higher received SNR is selected and used for datareception of the current frame. Another switching technique can be toselect the antenna independently at each sub-carrier (or combine the twoobservations). However, this can increase receiver complexity, since itmay employ a second set of RF chains, having two FFT blocks at thebase-band and the per sub-carrier antenna selection logic.

It is noted that in another approach, an antenna switching scheme can bebased on effective SNR. The effective SNR is an indication of receivedsignal quality when the channel realization varies across a code word(due to time-variation or frequency variation or both). The effectiveSNR can be a monotonous function of the average constrained capacity.For an OFDM symbol, the average constrained capacity for a set ofsubcarriers with a common modulation scheme m is calculated as thefollowing: $\begin{matrix}{C_{i} = {\frac{1}{N_{c}}{\sum\limits_{k = 0}^{N_{c} - 1}{\phi_{m}( \frac{{H_{i,k}}^{2}}{\sigma^{2}} )}}}} & (1)\end{matrix}$

where H_(i,k) is a channel estimate for subcarrier k of OFDM symbol i,and σ² is the variance of the additive noise/interference. Theconstrained capacity function φ_(m)(.) generally depends on themodulation scheme m, e.g., QPSK, 16QAM, and so forth. The averageconstrained capacity is a monotonous function of the effective SNR, withhigher effective SNR representing higher average constrained capacity.Therefore, antenna selection can be determined by the averageconstrained capacity. In this scheme, the average constrained capacitycan be calculated for the preamble symbols reserved for antennaselection for both antennas based on the channel estimate and noisevariance estimate according Equation (1). The antenna with higheraverage constrained capacity (hence higher effective SNR) can beselected and used for data reception. For the case in which thesubcarriers for the OFDM symbol of interest are modulated by differentmodulation schemes, one possibility of the antenna selection is based onthe average constrained capacity of the subcarriers with the lowestmodulation size. In this case, the summation in Equation (1) should beover the subcarriers with the lowest modulation size.

In addition to switching diversity provided at 120 between antennas inthe subset 110, a maximum ratio combining (MRC) technique for a FLO-likebroadcast OFDM system is provided at the configuration 160. Beingdifferent from the switching diversity scheme which selects the antennawith stronger RSSI or higher SNR for reception and demodulation based onthe overall received power at each antenna at 120, maximum ratiocombining combines received signals from the designated antennas in thesubset 110 independently at each sub-carrier post Fast Fourier Transform(FFT) processing. An example diagram of an MRC in a FLO-like OFDM systemis illustrated in FIG. 4, whereas an example switching diversity systemis illustrated in FIG. 2.

As noted above, one approach for signal processing is to have at leasttwo separate antennas on a receiver handset. For simplicity, thefollowing discussion is related to having two receive antennas, howeverit is to be appreciated that the systems and methods described hereincan be readily generalized to more than two receive antennas in thesubset 110. In addition, though the system 100 is motivated in part bythe desire to improve performance at low Doppler spreads, it is notgenerally coupled to Reed-Solomon (R-S) coding and facilitates signalperformance even when such coding is absent. For FLO-like OFDM broadcastsystems, typically a fraction of the frame duration is used to transmitpackets of interest to the receiver. These packets could correspond toparticular content being broadcast, and multiple content channels can bemultiplexed into the respective frame. These set of packets of interestcan be referred to as an MLC (Multicast Logical Channel). To reducepower consumption, the receiver is typically operating during the OFDMsymbols of interest and a small number of preamble and post-amblesymbols for the frame.

FIG. 2 illustrates an example receiver switching system 200 that employsmultiple antennas to enhance signal quality. Before proceeding, and asnoted above, the more than two antennas can be employed than shown inthe example switching system 200. Received signal strength can bemeasured on antennas 210 during preamble symbols of a current frame. Theantenna with the stronger received power is then selected and used fordata reception of the entire frame. Specifically in this example, one RFchain is implemented in the receiver. The RF chain includes a front-endRF filter, low noise amplifier (LNA) 224, mixer 230, analog base-bandlow-pass filter 234, an A/D converter 240, a digital filter 244, a DCcorrection component 250, and an automatic gain control (AGC) 254. Aswitch 260 connects one of the antennas 210 to the RF chain (e.g.,analog switch).

Typically, before the start of an MLC of a current frame, the AGC 254powers up and a first antenna 210 is connected to the RF chain. At theend of the AGC acquisition period, based on the information of thecurrent LNA gain state and the AGC loop accumulator, a received signalstrength indication (RSSI) of the first antenna is calculated at 264.Then, a second antenna is selected by the switch 260 and connected tothe RF chain. After the AGC acquisition period for the second antennaelapses, its RSSI is calculated at 264 and compared with that of thefirst antenna 210. The antenna with higher RSSI is selected and used fordata reception of the current frame. Therefore, at least two AGCacquisition periods of OFDM symbols can be employed to perform adecision on antenna selection prior to the subsequent preamble and MLCsymbols. To reduce receiver power consumption, during AGC acquisitionand RSSI measurement, successive blocks of AGC can be turned off. Analternative embodiment is to have two sets of RF chains and A/D, DC, andDGVA blocks implemented so that AGC acquisition and RSSI calculation forboth antennas can proceed concurrently as described below with respectto FIG. 4. This can save the time of one RSSI measurement period at thetrade-off of increased receiver complexity.

For the system 200, antenna switching is generally not allowed duringthe data demodulation of a frame. That is, antenna selection is madeonce per frame. An alternative method is to have other or higher antennaswitching rates such as once per MLC assuming a suitable gap betweenMLCs for antenna selection. This can also include switching during anMLC provided that time-averaging of the channel estimates is disabled.For very slow antenna selection rates, lesser diversity is realized infading channels since the selected antenna may not remain the bestantenna as the channel changes. Very high antenna switching rates couldhelp in continuing to provide antenna diversity at higher Dopplerspreads. However, switching an antenna during MLC demodulation coulddisrupt the base-band receiver operations such as AGC and channelestimation averaging. Switching at high rate can also increase thereceiver power consumption. As can be appreciated, the system 200 can beemployed as part of a wireless communications device. This can includemeans for monitoring a subset of antennas at a wireless device (e.g.,RSSI component 264), means for selecting one antenna from the subset ofantennas (e.g., Antenna analog switch 260); and means for processing asignal from the selected antenna (e.g., RF filter, low noise amplifier(LNA) 224, mixer 230, analog base-band low-pass filter 234, an A/Dconverter 240, a digital filter 244, a DC correction component 250, andan automatic gain control (AGC) 254).

Other components in the switching system 200 can include an automaticfrequency control (AFC) 270 that receives input from the DGVA 254.Output from the AFC 270 then feeds a sample buffer 272, a Fast FourierTransform (FFT) component 274, and a de-channelization component 276. Atiming component 278 and a channel estimation component 280 can beemployed as feedback elements. Other components in the switching system200 can include a decoding metric generator 282, a de-interleavingcomponent 284, a descrambling component 286, and a turbo decoder 288.

FIG. 3 illustrates example switching component processing 300 for awireless receiver. In the antenna diversity system discussed above inFIG. 2, at least two options are available for the operation of theantenna switching block at 260 of FIG. 2. One option at 310 is toperform antenna switching when the mobile receiver is moving at lowvehicular speed (or the Doppler spread is small). The other option at320 is to substantially always have switching turned on. Option 310 isdiscussed in more detail as follows.

The first switching processing option 310 may be of generally moreinterest when there is differential between two or more antennas. ForFLO systems, the primary antenna may have a gain that is approximately 5dB higher than the secondary antenna. The gain on the second antennacould be lesser because it is tuned to operate in different frequencyband (e.g., CDMA) or due to form factor considerations, for example. Byhaving the switching block always on, for high Doppler spread there is apossibility that the secondary antenna is chosen during RSSI measurementwhile it turns out that the primary antenna has stronger received powerduring most of the MLC of interest. As a result, turning on theswitching block only for low vehicular speed (small Doppler spread) canbe beneficial. A method can be adopted to estimate the Doppler spreadbased on channel estimates of adjacent OFDM symbols. Thus, the switchingdiversity block is turned on only when the channel time correlation ishigher than a pre-determined threshold. It is noted that a secondantenna if employed can be mounted internally due to form factorconsiderations.

FIG. 4 illustrates an example multi-path processing system 400 for awireless receiver system. In this example, two sets of analog RF chainsare illustrated at 410 and 414. The respective chains 410 and 414 caninclude SAW filters 420 and 422 which feed low noise amplifiers (LNA)424 and 426. Output from LNA 424 and 426 can feed mixer, analog LPF, andA/D blocks 428 and 430 which in turn feed digital filter/DC offsetblocks 432 and 434. Output from blocks 432 and 434 drive digitalvariable gain amplifiers (DGVA) 436 and 438 which also drive AFCcomponents 440 and 442, respectively. From the AFC components 440 and442, are sample buffers 450 and 442, FFT blocks 454 and 456, and channelestimation blocks 458 and 460. Feedback can be provided via timingblocks 462 and 464. Other components in the system 400 include a MaximalRatio Combining (MRC) block 466, a de-channelization component 468, adecoding metric generator 470, a de-interleaving component 472, adescrambling component 474, and a turbo decoder 476.

The receiver chains 410 and 414 operate concurrently during demodulationof MLC symbols of interest as well as demodulation of preamble andpost-amble symbols. Signal received on the antennas 416 and 418 areprocessed by the receiver chains 410 and 414 separately up to the outputof an FFT and channel estimation blocks at 480 and 482 respectively. TheFFT output and channel estimate of the receiver chains are then combinedat 466 (Maximal Ratio Combining (MRC) block) on a per sub-carrier basisto maximize signal-to-noise ratio and sent to successive blocks fordecoding at 468-476. Each receiver chain maintains its own LNA gainstate, DVGA gain, DC correction, frequency and time tracking, forexample.

At the FFT output at 480 and 482 respectively, let the received signalon the i-th sub-carrier be r_(i,1) and r_(i,2) for receiver chain #1 and#2, respectively, and the frequency-domain channel estimate ofsub-carrier i be c_(i,1) and c_(i,2) for receiver chain #1 and #2,respectively. The MRC block 466 combines the output of the two receiverchains for the i-th sub-carrier as following:y _(i) =c* _(i,1) r _(i,1) +c* _(i,2) r _(i,2),  (2)Where * denotes the complex conjugate. If the channel estimate isaccurate, the per sub-carrier combining of the received signal accordingto Eq. (1) is optimal in the sense that the signal-to-noise ratio ismaximized for each sub-carrier. Significant performance gain can berealized even if there is differential between the two receive antennas.It is noted that the example system 400 can be employed as part of awireless communications device. This can include means for receiving asignal at a wireless device from at least two signal sources (e.g.,antenna subset, blocks 410, 414), a means for processing the signal in afirst signal chain and a second signal chain (e.g., mixers, filters,amplifiers, buffers, frequency transform components, estimationcomponents and so forth). This can also include means for combining thefirst and the second signal chains (e.g., MRC 466).

FIG. 5 illustrates example network layers 500 for a wireless systemwhere data received there from may be employed in the frequency blocksdescribed above. A Forward Link Only (FLO) air interface protocolreference model is shown in FIG. 5. Generally, the FLO air interfacespecification covers protocols and services corresponding to OpenSystems Interconnect (OSI) networking model having Layers 1 (physicallayer) 502 and Layer 2 (Data Link layer) 504. The Data Link layer isfurther subdivided into two sub-layers, namely, Medium Access (MAC)sub-layer 506, and Stream sub-layer 508. Upper Layers 510 include OSIlayers 3-7 and can include compression of multimedia content, accesscontrol to multimedia, along with content and formatting of controlinformation. The MAC layer 506 includes multiplexing and Quality ofService (QoS) delivery functions 512. The MAC layer 506 also includeslogical channels 514.

The FLO air interface specification typically does not specify the upperlayers to allow for design flexibility in support of variousapplications and services. These layers are shown to provide context.The Stream Layer includes multiplexes up to three upper layer flows intoone logical channel, binding of upper layer packets to streams for eachlogical channel, and provides packetization and residual error handlingfunctions. Features of the Medium Access Control (MAC) Layer includescontrols access to the physical layer, performs the mapping betweenlogical channels and physical channels, multiplexes logical channels fortransmission over the physical channel, de-multiplexes logical channelsat the mobile device, and/or enforces Quality of Service (QOS)requirements. Features of Physical Layer include providing channelstructure for the forward link, and defining frequency, modulation, andencoding requirements

In general, FLO technology utilizes Orthogonal Frequency DivisionMultiplexing (OFDM), which is also utilized by Digital AudioBroadcasting (DAB), Terrestrial Digital Video Broadcasting (DVB-T), andTerrestrial Integrated Services Digital Broadcasting (ISDB-T).Generally, OFDM technology can achieve high spectral efficiency whileeffectively meeting mobility requirements in a large cell SFN. Also,OFDM can handle long delays from multiple transmitters with a suitablelength of cyclic prefix; a guard interval added to the front of thesymbol (which is a copy of the last portion of the data symbol) tofacilitate orthogonality and mitigate inter-carrier interference. Aslong as the length of this interval is greater than the maximum channeldelay, reflections of previous symbols are removed and the orthogonalityis preserved.

Proceeding to FIG. 6, a FLO physical layer 600 is illustrated. In anembodiment, a superframe is equal to 1200 OFDM symbols with a one secondtime duration. The FLO physical layer uses a 4K mode (yielding atransform size of 4096 sub-carriers), providing superior mobileperformance compared to an 8K mode, while retaining a sufficiently longguard interval that is useful in fairly large Single Frequency Networks.Rapid channel acquisition can be achieved through an optimized pilot andinterleaver structure design. The interleaving schemes incorporated inthe FLO air interface facilitate time diversity. The pilot structure andinterleaver designs optimize channel utilization without annoying theuser with long acquisition times. Generally, FLO transmitted signals areorganized into super frames as illustrated at 600. Each super frame iscomprised of four frames of data, including TDM pilots (Time DivisionMultiplexed) 604, Overhead Information Symbols (OIS) 606 and frames 608,610, 612, 614, containing wide-area 616 and local-area data 618. The TDMpilots are provided to allow for rapid acquisition of the OIS. The OISdescribes the location of the data for each media service in the superframe.

Typically, each super frame consists of 200 OFDM symbols per MHz ofallocated bandwidth (1200 symbols for 6 MHz), and each symbol contains 7interlaces of active sub-carriers. Each interlace is uniformlydistributed in frequency, so that it achieves the full frequencydiversity within the available bandwidth. These interlaces are assignedto logical channels that vary in terms of duration and number of actualinterlaces used. This provides flexibility in the time diversityachieved by any given data source. Lower data rate channels can beassigned fewer interlaces to improve time diversity, while higher datarate channels utilize more interlaces to minimize the radio's on-timeand reduce power consumption.

The acquisition time for both low and high data rate channels isgenerally the same. Thus, frequency and time diversity can be maintainedwithout compromising acquisition time. Most often, FLO logical channelsare used to carry real-time (live streaming) content at variable ratesto obtain statistical multiplexing gains possible with variable ratecodecs (Compressor and Decompressor in one). Each logical channel canhave different coding rates and modulation to support variousreliability and quality of service requirements for differentapplications. The FLO multiplexing scheme enables device receivers todemodulate the content of the single logical channel it is interested into minimize power consumption. Mobile devices can demodulate multiplelogical channels concurrently to enable video and associated audio to besent on different channels.

Error correction and coding techniques can also be employed. Generally,FLO incorporates a turbo inner code13 and a Reed Solomon (RS) 14 outercode. Typically, the turbo code packet contains a Cyclic RedundancyCheck (CRC). The RS code need not be calculated for data that iscorrectly received, which, under favorable signal conditions, results inadditional power savings. Another aspect is that the FLO air interfaceis designed to support frequency bandwidths of 5, 6, 7, and 8 MHz. Ahighly desirable service offering can be achieved with a single RadioFrequency channel.

FIG. 7 illustrates a multi-antenna process 700 for wireless receiversystems. While, for purposes of simplicity of explanation, themethodology is shown and described as a series or number of acts, it isto be understood and appreciated that the processes described herein arenot limited by the order of acts, as some acts may occur in differentorders and/or concurrently with other acts from that shown and describedherein. For example, those skilled in the art will understand andappreciate that a methodology could alternatively be represented as aseries of interrelated states or events, such as in a state diagram.Moreover, not all illustrated acts may be required to implement amethodology in accordance with the subject methodologies disclosedherein.

Proceeding to 710, an antenna subset is selected. As previously noted,at least two antennas are typically employed for the antenna subset butmore than two antennas are possible. Based on a desired receiverconfiguration, two processing paths are possible for the determinedantenna subset at 714 and 718. If the process path 718 is selected,signals from the antenna subset 710 are monitored measured or sampledfor various signal parameters such as received signal strength orsignal-to-noise ratio. At 730, based on the measurements at 720, anantenna is selected from the subset for receiving a wireless signal. Aspreviously noted, switching decisions can be performed at differenttimes and under differing situations. For instance, in some cases,switching decisions may be performed during specified times such asduring detected movement of a receiver. In other cases, monitoring andswitching of antennas may be performed at regular intervals such asbetween super frames or between super frame subsets. At 740, signalsfrom the selected antenna are processed through the respective receiver.This can include amplifying, mixing, digital or analog conversions,filtering, gain controlling, FFT computations, channel estimations,buffering, decoding, descrambling, and so forth.

If the path at 718 is taken in the process 700, a separate signalprocessing path can be assigned for each antenna employed by thereceiver at 750. Such processing paths for the respective antennas caninclude filters, mixers, amplifiers, gain controllers, buffers, timingcomponents, FFT components, and channel estimation components, forexample. At 760, outputs from the individual processing paths arecombined. Such combining can include analog processes, digitalprocesses, or a combination thereof and include processes such asmaximal ratio combining, for example. At 770, the combined signals fromthe respective antenna subset and signal processing paths are furtherprocessed in a wireless receiver. Such processing can includede-channelization, decoding, de-interleaving, descrambling, and soforth.

FIG. 8 is an illustration of a user device 800 that is employed in awireless communication environment, in accordance with one or moreaspects set forth herein. User device 800 comprises a receiver 802 thatreceives a signal from, for instance, a receive antenna (not shown), andperforms typical actions thereon (e.g., filters, amplifies, downconverts, etc.) the received signal and digitizes the conditioned signalto obtain samples. Receiver 802 can be a non-linear receiver, such as amaximum likelihood (ML)-MMSE receiver or the like. A demodulator 804 candemodulate and provide received pilot symbols to a processor 806 forchannel estimation. A FLO channel component 810 is provided to processFLO signals as previously described. This can include digital streamprocessing and/or positioning location calculations among otherprocesses. Processor 806 can be a processor dedicated to analyzinginformation received by receiver 802 and/or generating information fortransmission by an optional transmitter 816, a processor that controlsone or more components of user device 800, and/or a processor that bothanalyzes information received by receiver 802, generates information fortransmission by transmitter 816, and controls one or more components ofuser device 800.

User device 800 can additionally comprise memory 808 that is operativelycoupled to processor 806 and that stores information related tocalculated ranks for user device 800, a rank calculation protocol,lookup table(s) comprising information related thereto, and any othersuitable information for supporting list-sphere decoding to calculaterank in a non-linear receiver in a wireless communication system asdescribed herein. Memory 808 can additionally store protocols associatedrank calculation, matrix generation, etc., such that user device 800 canemploy stored protocols and/or algorithms to achieve rank determinationin a non-linear receiver as described herein.

It will be appreciated that the data store (e.g., memories) componentsdescribed herein can be either volatile memory or nonvolatile memory, orcan include both volatile and nonvolatile memory. By way ofillustration, and not limitation, nonvolatile memory can include readonly memory (ROM), programmable ROM (PROM), electrically programmableROM (EPROM), electrically erasable ROM (EEPROM), or flash memory.Volatile memory can include random access memory (RAM), which acts asexternal cache memory. By way of illustration and not limitation, RAM isavailable in many forms such as synchronous RAM (SRAM), dynamic RAM(DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM),enhanced SDRAM (ESDRAM), Synchlink DRAM (SLDRAM), and direct Rambus RAM(DRRAM). The memory 808 of the subject systems and methods is intendedto comprise, without being limited to, these and any other suitabletypes of memory. User device 800 further comprises a background monitor814 for processing FLO data, a symbol modulator 814 and a transmitter816 that transmits the modulated signal.

FIG. 9 is an illustrates an example system 900 that comprises a basestation 902 with a receiver 910 that receives signal(s) from one or moreuser devices 904 through a plurality of receive antennas 906, and atransmitter 924 that transmits to the one or more user devices 904through a transmit antenna 908. Receiver 910 can receive informationfrom receive antennas 906 and is operatively associated with ademodulator 912 that demodulates received information. Demodulatedsymbols are analyzed by a processor 914 that is similar to the processordescribed above with regard to FIG. 8, and which is coupled to a memory916 that stores information related to user ranks, lookup tables relatedthereto, and/or any other suitable information related to performing thevarious actions and functions set forth herein. Processor 914 is furthercoupled to a FLO channel 918 component that facilitates processing FLOinformation associated with one or more respective user devices 904.

A modulator 922 can multiplex a signal for transmission by a transmitter924 through transmit antenna 908 to user devices 904. FLO channelcomponent 918 can append information to a signal related to an updateddata stream for a given transmission stream for communication with auser device 904, which can be transmitted to user device 904 to providean indication that a new optimum channel has been identified andacknowledged. In this manner, base station 902 can interact with a userdevice 904 that provides FLO information and employs a decoding protocolin conjunction with a non-linear receiver, such as an ML-MIMO receiver,and so forth.

FIG. 10 shows an exemplary wireless communication system 1000. Thewireless communication system 1000 depicts one base station and oneterminal for sake of brevity. However, it is to be appreciated that thesystem can include more than one base station and/or more than oneterminal, wherein additional base stations and/or terminals can besubstantially similar or different for the exemplary base station andterminal described below.

Referring now to FIG. 10, on a downlink, at access point 1005, atransmit (TX) data processor 1010 receives, formats, codes, interleaves,and modulates (or symbol maps) traffic data and provides modulationsymbols (“data symbols”). A symbol modulator 1015 receives and processesthe data symbols and pilot symbols and provides a stream of symbols. Asymbol modulator 1020 multiplexes data and pilot symbols and providesthem to a transmitter unit (TMTR) 1020. Each transmit symbol may be adata symbol, a pilot symbol, or a signal value of zero. The pilotsymbols may be sent continuously in each symbol period. The pilotsymbols can be frequency division multiplexed (FDM), orthogonalfrequency division multiplexed (OFDM), time division multiplexed (TDM),frequency division multiplexed (FDM), or code division multiplexed(CDM).

TMTR 1020 receives and converts the stream of symbols into one or moreanalog signals and further conditions (e.g., amplifies, filters, andfrequency up converts) the analog signals to generate a downlink signalsuitable for transmission over the wireless channel. The downlink signalis then transmitted through an antenna 1025 to the terminals. Atterminal 1030, an antenna 1035 receives the downlink signal and providesa received signal to a receiver unit (RCVR) 1040. Receiver unit 1040conditions (e.g., filters, amplifies, and frequency down converts) thereceived signal and digitizes the conditioned signal to obtain samples.A symbol demodulator 1045 demodulates and provides received pilotsymbols to a processor 1050 for channel estimation. Symbol demodulator1045 further receives a frequency response estimate for the downlinkfrom processor 1050, performs data demodulation on the received datasymbols to obtain data symbol estimates (which are estimates of thetransmitted data symbols), and provides the data symbol estimates to anRX data processor 1055, which demodulates (i.e., symbol de-maps),de-interleaves, and decodes the data symbol estimates to recover thetransmitted traffic data. The processing by symbol demodulator 1045 andRX data processor 1055 is complementary to the processing by symbolmodulator 1015 and TX data processor 1010, respectively, at access point1005. Other components that may be provided include a TX data processor1060, a symbol modulator 1065, a transmitter unit 1070, a receiver unit1075, a symbol demodulator 1080, an RX data processor 1085, and aprocessor 1090.

Processors 1090 and 1050 direct (e.g., control, coordinate, manage,etc.) operation at access point 1005 and terminal 1030, respectively.Respective processors 1090 and 1050 can be associated with memory units(not shown) that store program codes and data. Processors 1090 and 1050can also perform computations to derive frequency and impulse responseestimates for the uplink and downlink, respectively.

For a multiple-access system (e.g., FDMA, OFDMA, CDMA, TDMA, etc.),multiple terminals can transmit concurrently on the uplink. For such asystem, the pilot subbands may be shared among different terminals. Thechannel estimation techniques may be used in cases where the pilotsubbands for each terminal span the entire operating band (possiblyexcept for the band edges). Such a pilot subband structure would bedesirable to obtain frequency diversity for each terminal. Thetechniques described herein may be implemented by various means. Forexample, these techniques may be implemented in hardware, software, or acombination thereof. For a hardware implementation, the processing unitsused for channel estimation may be implemented within one or moreapplication specific integrated circuits (ASICs), digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), processors, controllers, micro-controllers, microprocessors,other electronic units designed to perform the functions describedherein, or a combination thereof. With software, implementation can bethrough modules (e.g., procedures, functions, and so on) that performthe functions described herein. The software codes may be stored inmemory unit and executed by the processors 1090 and 1050.

For a software implementation, the techniques described herein may beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The software codes may be storedin memory units and executed by processors. The memory unit may beimplemented within the processor or external to the processor, in whichcase it can be communicatively coupled to the processor via variousmeans as is known in the art.

What has been described above includes exemplary embodiments. It is, ofcourse, not possible to describe every conceivable combination ofcomponents or methodologies for purposes of describing the embodiments,but one of ordinary skill in the art may recognize that many furthercombinations and permutations are possible. Accordingly, theseembodiments are intended to embrace all such alterations, modificationsand variations that fall within the spirit and scope of the appendedclaims. Furthermore, to the extent that the term “includes” is used ineither the detailed description or the claims, such term is intended tobe inclusive in a manner similar to the term “comprising” as“comprising” is interpreted when employed as a transitional word in aclaim.

1. A receiver processing method on a forward link of a multicastwireless network, comprising: receiving a signal from at least twoantennas across a wireless network; processing the signal in at leasttwo signal paths for the two antennas; and combining the signals at anoutput from the signal paths to facilitate signal reception for awireless device.
 2. The method of claim 1, the signal paths include atleast one of an A/D converter, a digital filter, a DC correction, a gainamplifier, a frequency control component, a Fast Fourier Transformcomponent, a synchronizer, and a channel estimator.
 3. The method ofclaim 2, further comprising demodulating multicast logical channelsymbols including preamble and post-amble symbols.
 4. The method ofclaim 1, further comprising processing one or more receiver chainsseparately up to an output of an FFT component and a channel estimationblock.
 5. The method of claim 4, further comprising combining the outputof the FFT component and the channel estimation block.
 6. The method ofclaim 5, further comprising combining the output of the FFT componentand the channel estimation block according to a Maximal Ratio Combining(MRC) algorithm on a per sub-carrier basis to maximize signal-to-noiseratio.
 7. The method of claim 5, further comprising maintaining a lownoise amplifier gain state, gain amplifier gain, DC correctionparameter, a frequency component or a time tracking parameter.
 8. Themethod of claim 5, the output of the FFT component includes an i-thsub-carrier composed of r_(i,1) and r_(i,2) for a receiver chain 1 and areceiver chain 2, respectively.
 9. The method of claim 8, furthercomprising determining a frequency-domain channel estimate ofsub-carrier i denoted as c_(i,1) , and c_(i,2) for the receiver chain 1and the receiver chain 2, respectively.
 10. The method of claim 9,further comprising signals from the receiver chain 1 and the receiverchain 2 according to the following equation:y _(i) =c _(i,1) *r _(i,1) +c _(i,2) *r _(i,2), where * denotes acomplex conjugate.
 11. The method of claim 10, further comprisingmaximizing a signal-to-noise ratio for a respective receiver chainsub-carrier.
 12. A computer readable medium having computer executableinstructions stored thereon to execute components of a wirelessreceiver, comprising: receiving a signal from two or more antennas in awireless receiver; processing the signal in at least two signal chainsin the wireless receiver; and combining output from the two signalchains according to a maximum ratio signal between the two signalchains.
 13. The computer readable medium of claim 12, further comprisingemploying at least one of a Fourier Transform component and a channelestimation component in the signal chains.
 14. The computer readablemedium of claim 12, further comprising a layer component having at leastone of a physical layer, a stream layer, a medium access layer, and anupper layer.
 15. The computer readable medium of claim 14, the physicallayer further comprising at least one of a frame field, a pilot field,an overhead information field, a wide area field, and a local areafield.
 16. The computer readable medium of claim 15, further comprisingan error correction field.
 17. A wireless communications apparatus,comprising: at least a first radio frequency processing channel toprocess a signal from at least one antenna from a subset of antennas; atleast a second radio frequency processing channel to process the signalfrom at least a second antenna from a subset of antennas; a memory thatincludes a component to determine signal quality for the subset ofantennas; and a processor that facilitates signal processing for atleast one wireless apparatus associated with the subset of antennas. 18.The apparatus of claim 17, further comprising one or more components todecode a Forward Link Only data stream.
 19. The apparatus of claim 17,the processor is employed to process at least one communication layer ina group of layers.
 20. A wireless communications device, comprising:means for receiving a signal at a wireless device from at least twosignal sources; means for processing the signal in a first signal chain;means for processing the signal in a second signal chain; and means forcombining the first and the second signal chains.
 21. The device ofclaim 20, further comprising at least a third signal chain and at leasta third signal source.
 22. The device of claim 20, the signal chainsinclude at least one of an A/D converter, a digital filter, a DCcorrection component, a gain amplifier, a frequency control component, aFast Fourier Transform component, a synchronizer, and a channelestimator.
 23. The device of claim 20, further comprising demodulatingone or more signal chain channel symbols.
 24. The device of claim 20,further comprising processing one or more signal chains separately up toan output of an FFT component and a channel estimation block.
 25. Thedevice of claim 24, further comprising combining the output of the FFTcomponent and the channel estimation block according to a Maximal RatioCombining (MRC) routine.
 26. The device of claim 25, further comprisingprocessing a low noise amplifier gain state, a DC correction parameter,a frequency component or a time tracking parameter.